1. Field of the Invention
The disclosures herein generally relate to a polarizing apparatus and a polarizing method.
2. Description of the Related Art
A piezoelectric material is used for various devices including sensors or actuators because the piezoelectric material has a property of converting a displacement or a pressure to an electrical signal and a property of converting the electric signal to the displacement or the pressure. For example, PZT is used as the piezoelectric material.
A Chemical Solution Deposition (CSD) method, a sputtering method, a Chemical Vapor Deposition (CVD) method, or the like is used as a method for creating a PZT crystal film, which is a piezoelectric film. In particular, in comparison with other methods, the CSD method is widely used as an extremely effective method of forming the film because the CSD method has a merit of being able to uniformly coat, in a wide area at low cost, a multicomponent oxide in composition as designed.
When the CSD method is used to create the PZT crystal film, a chemical liquid such as sol-gel (SG) liquid of PZT, for example, is applied onto a substrate. After a drying treatment is performed, the substrate is externally heated by an electric furnace, a Rapid Thermal Annealing (RTA) apparatus, or the like to perform a several minutes heating treatment at a temperature equal to or higher than 600° C. to crystallize the film. Processes of the application, the drying treatment, and the crystallization are repeatedly performed to create a thick film.
When the PZT crystal film is used to create a piezoelectric device having high safety, it is required to apply an appropriate electric field to the PZT crystal film and to perform polarization processing. The polarization processing is sometimes referred to as a polling processing, an aging processing, or the like.
For example, Japanese Examined Patent Publication No. 5410686 discloses a process for producing a piezoelectric film having spontaneous polarization. According to the process disclosed in Japanese Examined Patent Publication No. 5410686, a piezoelectric film is formed by a sputtering method at a film formation temperature equal to or higher than a Curie point. After the film formation and before the temperature of the piezoelectric film becomes equal to or lower than the Curie point, application of an electric field to the piezoelectric film from outside is started and polarization processing is performed until the temperature of the piezoelectric film becomes equal to or lower than the Curie point.